The ionospheric feedback instability describes the fast, spontaneous break-up of large-scale field-aligned currents flowing through a low-conductivity ionosphere. Since the seminal paper by Atkinson in 1970, the ionospheric feedback instability and its small-scale Alfvén-wave currents have been postulated as an important pathway to the formation of small-scale structures in auroral arcs. Previous modeling efforts of this instability are all based on a flat-sheet, height-integrated ionosphere approximation. Sydorenko and Rankin [2017] are the first to apply a simplified but more realistic ionosphere that varies with height. It shows that, in the height-resolved E-layer, the vertical shear in the horizontal ion flow velocity stretches plasma density perturbations in the horizontal direction and thus has a stabilizing effect on the instability. This study represents a significant development, with important implications for the well-developed theory on the auroral arc formation.

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